Imaging method utilizing chemical reactivities of photoexcited states of aromatic hydroxy compounds

ABSTRACT

An imaging process employing the excited state reactivities of aromatic hydroxy materials to produce a visible image.

United Statesv Patent 1191 Saeva et al.

1111 3,801,319 [451 Apr. 2, 1974 [75] Inventors: Franklin D. Saeva,Fairport; Donald E; Sargent, Schenectady, both of N.Y.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

22 Filed: June 21, 1972 21 Appl.No.:265.,053

I [52] US. Cl. 96/27 R, 96/48 R, 96/49,

[51] Int. Cl. G03c 5/04 [58] Field of Search, 96/48 R, 49, 90 R, 91 R,96/48 HD, 27 R; 117/368, 36.9; 25/65 T [56] References Cited UNITEDSTATES PATENTS 1,776,155 9/1930 Kogel 96/90 R X 2,082,178 6/1937 Ochwat96/90 R X 2,306,471 12/1942 Soloman 96/91 R X 2,405,523 8/1946 Sease eta1. 96/91 R X 2,411,811 11/1946 Sargent 96/90 R X 2,416,021 2/1947Schoer.... 96/90 R X 3,218,166 11/1965 Reitter 117/368 X 3,367,7972/1968 Sorensen 117/36.8 3,490,907 1/1970 Schenck et al..... 96/90 R X3,647,448 3/1972 DeMeyer et al. 96/90 R X 3,694,247 9/1972 Desjarlais117/36.8-X

Primary ExaminerChar'les L. Bowers, Jr.

[5 7] ABSTRACT An imaging process employing the excited statereactivities of aromatic hydroxy materials to produce a visible image.

17 Claims, N0 Drawings 'trites.

IMAGING METHOD UTILIZING CHEMICAL REACTIVITIES OF PHOTOEXCITED STATES OFAROMATIC HYDROXY COMPOUNDS BACKGROUND OF THE INVENTION This inventionrelates, in general, to a novel imaging process which utilizes theincreased chemical reactivity of hydroxy aromatic compounds when theyare subjected to photoexcitation and, more specifically, this inventionrelates to a novel imaging process in which hydroxy aromatic compoundsare photoexcited in the presence of an inorganic or organic nitrite.

In the conventional diazo system, a substrate is coated with acomposition comprising two components, a diazonium compound which issensitive to light, and the other component is an azo coupler. In makinga print, the substrate is exposed to ultraviolet rays through themaster. The rays destroy or otherwise inactivate the print formingcomponents in all areas of coated material which are not protected bythe lines of design of the original. However, the problem of diazotypematerials is that they are notoriously difficult to store for longperiods prior to use. The phenomenon known as pre-coupling invariablyoccurs even in the absence of a developing agent such as, ammonia, etc.Moreover, because the diazonium compound and the azo dye couplingcomponent react slowly to form an azo dye, it is less useful forsubsequent copying purposes. Furthermore, diazo-type materials havealmost invariably given images of poor light fastness.

SUMMARY OF THE INVENTION It is, therefore, an object of this inventionto overcome the above-noted deficiencies.

Another object of this invention is to provide a simple, convenientimaging system.

Still another object of this invention is to provide photoprintingmaterials which have good storage stability prior to use.

A still further object of this invention is to accomplish the aboveobjects through the utilization of the enhanced chemical activity ofphotoexcited aromatic compounds in the presence of inorganic or organicni- Other objects will be apparent to those skilled in the photoprintingart from the following description of the invention.

In general,the present invention comprises the discovery that an hydroxyaromatic compound in the presence of inorganic or aliphatic nitrites andin the absence of acid can be made to undergo a photoinduced couplingreaction when light is absorbed to produce a colored reaction product inan imaging configuration.

In effect, what is occurring is that nitrous acid ordinarily required inthe conventional method of producing a coupling reaction is now beinggenerated via the photoexcitation of a hydroxy aromatic compound. Thephotoexcited aromatic specie has an increased acidity causing theformation of nitrous acid from nitrites as required for the couplingreaction.

Photoprinting materials employing the process of this invention haveseveral advantages over previously utilized materials. The materialsutilizing the process of this invention are quite stable in dark storageprior to use. In diazo-type materials a chemically energetic specie, thediazonium compound,'is always present in the copying material as made.In the materials utilizing the process of this invention, no chemicallyenergetic specie is present until the material is exposed," i.e., untilthe components are subjected to photoexcitation. With the process ofthis invention, very light fastness images can be obtained. Stillfurther, no obnoxious developing agents such as, ammonia, is required inthe processing of the materials of this invention.

The process of this invention may be utilized to prepare, negativeprint-out materials. In this embodiment ,the process of this inventionmay be compared to the blue printing process. But, in contrast to blueprinting materials, no cyanide-containing light sensitive materials needbe employed. In addition, the process of this invention provides meansof producing images of an almost unlimited range of colors. It shareswith blue printing the possible incorporation of very simple fixingmethods, such as washing the photoprinting material with water.

Photoprinting materials utilizing the process of this invention requireno complex or expensive machines for their exposure, development orfixing. This is in marked contrast to certain currently usedphotoprinting and copying methods. No equipment employing high voltages,powdered toners, developing fluids, fusing stations, etc., is required.

The process of this invention yields well defined images. No thermaltransfer steps are required. Thermal transfer almost invariably causesloss of definition and blurry images.

Finally, the process of this invention utilizes relatively low costmaterials. No silver salts or other expensive components are required.

More specifically, the process according to this invention comprisesforming a mixture of a hydroxy aromatic compound, e.g., 2-naphthol,inorganic or aliphatic nitrite, e.g., sodium nitrite, and optionally apolymeric matrix such as, polyvinyl pyrrolidone, dissolved in aqueousalcohol solvent to form a colorless solution. The polyvinyl pyrrolidoneserves as a polymeric matrix for the hydroxy aromatic compound andnitrite when the solvent is evaporated producing a selfsupportingcolorless film or the mixture may be uniformly coated onto a suitablesubstrate. In the absence of light, proton transfer essentially does nottake place between the hydroxy aromatic compound and the nitrite saltand no reaction occurs between the two components. However, when thehydroxy aromatic compound is photoexcited with light of a suitablewavelength corresponding to its ultraviolet absorption spectrum, protontransfer occurs rapidly and nitrous acid is generated. Reaction ofnitrous acid with the ground state of 2-naphthol provides the highlycolored 1- nitroso-2-naphthol.

The most probable mechanism of the reaction is that nitrous acid reactswith the ground state hydroxy aromatic compound as opposed to theexcited species providing the colored nitroso derivative. This is basedon the fact that the concentration of the excited state species is verymuch smaller than that of the ground state hydroxy aromatic material andthat the probabilities of molecular collision are enhanced for theground state material.

Additionally, if a metallic salt capable of reacting with the nitrosatednaphthol, such as a ferrous salt, is also present, a darker coloredimage (e.g., blue-green) can be formed and this exhibits excellent lightfastness.

Any suitable metallic salt may be used. Typical examples are the metalsalts of copper, iron, cobalt and zirconium.

Any suitable hydroxy aromatic compound may be employed. Typical examplesare hydroxy substituted: benzene, naphthalene, anthracene,phenanthracene, naphthacene, biphenyl, durene, acenaphthene, pyrene,chrysene, fluorene, fluoranthene and indene. Furthermore, the hydroxyaromatic compounds may carry other substituents such as, alkyl groups,halo, nitro, cyano, alkoxy, thio, carboxylic or sulfonic acids and saltsthereof, esters and aldehydes.

Whereas coloration is produced by photoexcitation of a hydroxy aromaticcompound in the presence of a nitrite, the physical consequences of theacidity enhancement are additionally utilized. If a primary aromaticamine is also present together with the combination of hydroxy aromaticcompound and nitrite, then a highly colored azo compound can be formedupon photoexcitation. It may be assumed that the hydroxy aromaticcompound, upon photoexcitation, liberates nitrous acid from the nitritepresent, that the so-formed nitrous acid diazotizes the aromatic amineand that the resulting diazonium compound reacts with the hydroxyaromatic compound to yield an azo compound. But formally, it makeslittle difference if it is assumed that following the liberation of thenitrous acid it reacts with the hydroxy aromatic compound to produce anitroso compound which, in turn, reacts with the aromatic amine toproduce the azo compound. However, should the stoichiometry of themixture be such that incomplete utilization of the nitroso derivativeoccurs, further color formation may be induced by addition of a metallicsalt to the solution causing additional color changes. The followingreaction sequence illustrates the transformation that takes placewherein 5,, represents the ground state and S represents the excitedstate:

l. Photoexcitation OH OH ho C) 2. Proton Exchange 4. Diazotization 5.Coupling The above reaction sequence does efficiently utilize thephotogenerated acid since one mole of product is formed per mole of acidconsumed. A further increase in the overall efficiency of such systemscould be realized by employing reaction sequences that respond in acatalytic fashion to the presence of acidic protons. Thus, manyconversions could be effected following a single photo-chemical event.

Although the solutions which are used to coat substrates to preparephotoprint materials according to the process of this invention areprepared in the dark, care must be taken to avoid acidity. Any acidityintroduced except that resulting from imagewise photoexcitation willobviously negate the principles upon which this invention is based. Inmaintaining the pH of the requisite coating solutions at approximately 7or slightly above,

buffers may be advantageously used.

In practicing another specific aspect of the present invention, an aminohydroxy aromatic compound has been found to undergo diazotization andself-coupling after being exposed imagewise to give a colored image.Accordingly, 8-amino-l-naphthol-3,6-disulfonic acid disodium salt ismixed in an aqueous solution of sodium nitrite which is coated ontopaper, air dried and then exposed imagewise with a suitable lightsource; nitrous acid is again produced in the system causing adiazotization and self-coupling reaction which results in the formationof a colored image.

Any suitable hydroxy aromatic compound also containing a primary aminofunction may be employed. Typical examples of the amino substitutedaromatic hydroxy compounds such as, benzene, naphthalene, anthracene,phenanthracene, naphthacene, biphenyl, durene, acenaphthene, pyrene,chrysene, fluorene, fluroanthene, and indene. Moreover, the aminoaromatic hydroxy compound may be further substituted with derivativessuch as, alkyl groups, halo, nitro, cyano, alkoxy, thio, acids, estersand aldehydes.

In preparing photoprinting materials utilizing the process of thisinvention certain coating aids may be added to the coating solutions.Thus, polymer thickening or sizing materials such as, polyvinylpyrrolidone, polyvinyl alcohol, gelatin, crosslinking agents such as,starch anthranilate, modified starch, etc., or the like may beadvantageously employed in order to obtain rapid print out, scuffresistant, optically attractive coatings. Likewise, colloidal materialssuch as, fillers or pigments, may be added. Among these are finelydivided silica, titanium dioxide, clays and the like. Any suitablesubstrate may be used. Typical examples of substrates may consist ofpaper, either coated or uncoated; plastic sheeting, either transparentor opaque; metallic sheets, foils, laminates, etc.

The coating process employed may include roller coating, knife coating,nib coating, dip coating, spraying, brushing, etc.

Since the active materials are usually coated from solution orsuspension in a liquid rather than from the dry powdered state, it isusually necessary to dry the photoprint material so prepared prior tocutting and packaging. It is possible, of course, to apply the requisitecombination of materials as dry particulate materials to suitablesubstrates.

In practicing the process of this invention, in contradistinction to theconventionaldiazo system, the substrate is exposed to light in anegative working system and in the areas where light strikes colorationis effected. Light, as previously stated, causes the hydroxy aromaticcompound in its excited state to produce nitrous acid from an inorganicor aliphatic nitrite which causes the coupling reaction to occur. Thewavelength of light usable in this invention must be absorbed by thehydroxy aromatic compound.

In a print-out image forming procedure of this type, a means ofstabilizing or fixing must be provided, otherwise the entire sheet ofphotoprint material slowly becomes colored upon exposure to room light.It has been found that simply washing the substrate with water, therebydissolving away the nitrite, constitutes one effective fixing procedure.By suitable choice of hydroxy aromatic compound, the remaining unreactedaromatic compound may also be removed by water washing from those areaswhere it has not been utilized in image formation. The colored image,being much less water soluble, usually remains on the substrate. On theother hand, when hydroxy aromatic compound and nitrite esters arepresent, fixation may be accomplished by sublimation or heating thesubstrate to a temperature which causes the unreacted material tosublime therefrom. Other fixing procedures will be obvious to thoseskilled in the art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following preferredexamples further define, describe and compare preferred materials,methods and techniques of the present invention.

EXAMPLE 1 Equal molar quantities of 2-naphthol, aniline and sodiumnitrite (0.001 mole) are dissolved in 100 ml of water previouslyadjusted to pI-l=7.0 being careful not to expose the solution toultraviolet irradiation. The mixture must be prepared and kept in thedark to avoid color formation prior to the exposure step. The watersolution is then applied to a hydrophilic paper substrate, and the wateris allowed to evaporate so that the substrate is dry to the touch. Thecoated substrate is then exposed in an imagewise fashion through atarget for 30 seconds using a 100 watt UV source positioned 1 inch awayfrom the substrate. After exposure the excess sodium nitrite is thenremoved in the fixing step by washing the substrate with water. Thepaper can then be dried in room light.

EXAMPLE II Equal molar quantities of Z-naphthol, aniline and sodiumnitrite (0.001 mole) and polyvinylpyrrolidone are dissolved in 100 ml of50/50 water-ethanol mixture being careful not to expose the solution toultraviolet irradiation. The mixture must be prepared and kept in thedark to avoid color formation prior to the exposure UV source positioned1 inch away from the substrate.

After exposure a mylar film is placed over the image to prevent furtherdevelopment of the background areas.

EXAMPLE Ill 8-amino-l-naphthol-3,6-disulfonic acid monosodium salt (lg)is dissolved in 50 cc of water and the solution adjusted to pI-I=7.0with either dilute (10 percent) hydrochloric acid or sodium hydroxidesolution (10 percent) as required. Sodium nitrite (1.0 gm) is then dissolved in 1.0 cc of water. The two solutions are then mixed in the darkand applied to a sheet of plain white paper with a brush. The watersolvent is allowed to evaporate at room temperature by passing dry airover the coated sheets. The dried paper, positioned 1 inch from anultraviolet (100 watt) light source is then exposed in an imagewisefashion for 30 seconds and the blue image fixed by washing away anyunreacted sodium nitrite with water.

EXAMPLE IV Equal molar quantities of 2-naphthol and isoamyl nitrite(0.001 mole) are dissolved in a 50/50 ethanolwater mixture (5 cc) alongwith 2.0 gm of polyvinylpyrrolidone being careful not to expose thesolution to ultraviolet irradiation. The solution is applied to a sheet.

of aluminum, the solvent allowed to dry and the coating exposed toultraviolet irradiation in an imagewise fashion for 30 seconds using a100 watt (3,000A) light source. Fixing of the yellow image isaccomplished by at least one of the reactants by sublimation.

EXAMPLE V Starch anthranilate (1) is prepared by heating potato starch(6.0 gm), sodium carbonate (0.012 gm) and isatoic anhydride (0.012 gm)in 9 ml of water for 4 hours at C. Plain white paper is then coated withthe starch (l) and the water solvent allowed to evaporate. The coatedpaper is then treated with a water solution of 2-naphthol-6-sulfonicacid sodium salt and sodium nitrite (0.1 gm of each in 5 cc of water)under red light conditions. The water is allowed to dry before beingcontact exposed to ultraviolet light in an imagewise fashion wattultraviolet light source [3,000A]) for 60 seconds. The resulting orangeimage is fixed by washing away unreacted naphthol and nitrite salts.

While the invention has been described with reference to its preferredembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents substituted for elementsthereof without departing from the true spirit and scope of theinvention. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the inventionwithout departing from its essential teachings.

What is claimed is:

1. An imaging process which comprises exposing in an imagewise manner acomposition comprising an aromatic hydroxy compound and an inorganic oraliphatic nitrite salt in aqueous solution to light of a suitablewavelength corresponding to the ultraviolet absorption pattern of thehydroxy aromatic compound, said process being further described in thatthe composition is droxy compound is substituted with an amino radical.

4. The process of claim 1 wherein the solution contains a metallic saltin addition to the aromatic hydroxy compound and the nitrite salt.

5. The process of claim 1 wherein the solution has a pH within the rangeof from 6 to 8.

6. An imaging process employing the excited state reactivities of anaromatic hydroxy material comprising the following steps:

a. providing an aromatic hydroxy compound;

b. combining said hydroxy compound with an inorganic or aliphaticnitrite salt in aqueous solution, said solution being characterized inthat it contains no ingredient which produces acid in the absence oflight of a suitable wavelength corresponding to the ultravioletabsorption spectrum of the aromatic hydroxy compound;

0. coating a substrate with said solution, and

d. exposing said coated substrate to light of a suitable wavelengthcorresponding to the ultraviolet absorption pattern of the hydroxyaromatic compound in an imagewise fashion to produce a colored image inthe exposed areas.

7. A process according to claim 6 wherein the image is fixed to saidcoated substrate.

8. A process according to claim 6 wherein an aromatic amine is includedin said solution.

9. A process according to claim 6 wherein the hydroxy aromatic compoundis substituted with an amino radical.

10. A process according to claim 6 wherein addition- 5 ally a metallicsalt is added to said solution.

11. A process according to claim 6 wherein said solution has a pH ofabout 6-8.

12. A process according to claim 6 wherein a crosslinking agent isincluded in said solution.

13. A process for producing a colored image comprising:

a. forming a solution by dissolving a hydroxy aromatic compound, amaterial selected from the group consisting of an inorganic or aliphaticnitrite or mixtures thereof, and a resinous polymer in a solvent, saidsolution being characterized in that it contains no ingredient whichproduces acid in the absence of light of a suitable wavelengthcorresponding to the ultraviolet absorption spectrum of the aromatichydroxy compound;

b. evaporating said solution to form a self-supporting colorless film,and

c. exposing said film in an imagewise fashion to light of a suitablewavelength corresponding to the ultraviolet absorption pattern of thehydroxy aromatic compound to thereby produce a colored image in theexposed areas.

14. A process according to claim 13 wherein said image is fixed in saidfilm.

15. A process according to claim 13 wherein an aromatie amine isincluded in said solution.

16. A process according to claim 13 wherein the hydroxy aromaticcompound is substituted with an amino radical.

17. A process according to claim 13 wherein a metallic salt is added tosaid solution.

Patent No. 3'8Ol'3l9 Dated pr l 2, 1974 lnventofls) Franklin Saeva andDonald E. Sargent It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

1. Column 1, line 1Q, omit "the other component is".

2. Column 1, line 18, "the master" should be "a master".

3. Column 1, line 49, "an hydroxy aromatic" should be "a hydroxyaromagic.

l 4. Column 2, line 6, "agents" should be "agent".

5. Column 2, line 11, "process. But should be "process, but" 6. Column7, line 1," "solution" should be "composition".

7. Column 7, line 4, "in" should be "in the" 8. Column 7, line 5, "asubstrate" should be "the substrate".

Signed and sealed this 17th day of September 1974.,

(SEAL) Attest:

MCCOY M. GIBSON JR. c. MARSHALL DANN attesting Officer Commissioner ofPatents FORM 1 USCOMM-DC 60376-P69 U.S. GOVERNMENT PRINTING OFFICE 19690366-334,

2. The process of claim 1 wherein the solution contains an aromaticamine in addition to the aromatic hydroxy compound and the nitrite salt.3. The process of claim 1 wherein the aromatic hydroxy compound issubstituted with an amino radical.
 4. The process of claim 1 wherein thesolution contains a metallic salt in addition to the aromatic hydroxycompound and the nitrite salt.
 5. The process of claim 1 wherein thesolution has a pH within the range of from 6 to
 8. 6. An imaging processemploying the exciteD state reactivities of an aromatic hydroxy materialcomprising the following steps: a. providing an aromatic hydroxycompound; b. combining said hydroxy compound with an inorganic oraliphatic nitrite salt in aqueous solution, said solution beingcharacterized in that it contains no ingredient which produces acid inthe absence of light of a suitable wavelength corresponding to theultraviolet absorption spectrum of the aromatic hydroxy compound; c.coating a substrate with said solution, and d. exposing said coatedsubstrate to light of a suitable wavelength corresponding to theultraviolet absorption pattern of the hydroxy aromatic compound in animagewise fashion to produce a colored image in the exposed areas.
 7. Aprocess according to claim 6 wherein the image is fixed to said coatedsubstrate.
 8. A process according to claim 6 wherein an aromatic amineis included in said solution.
 9. A process according to claim 6 whereinthe hydroxy aromatic compound is substituted with an amino radical. 10.A process according to claim 6 wherein additionally a metallic salt isadded to said solution.
 11. A process according to claim 6 wherein saidsolution has a pH of about 6-8.
 12. A process according to claim 6wherein a crosslinking agent is included in said solution.
 13. A processfor producing a colored image comprising: a. forming a solution bydissolving a hydroxy aromatic compound, a material selected from thegroup consisting of an inorganic or aliphatic nitrite or mixturesthereof, and a resinous polymer in a solvent, said solution beingcharacterized in that it contains no ingredient which produces acid inthe absence of light of a suitable wavelength corresponding to theultraviolet absorption spectrum of the aromatic hydroxy compound; b.evaporating said solution to form a self-supporting colorless film, andc. exposing said film in an imagewise fashion to light of a suitablewavelength corresponding to the ultraviolet absorption pattern of thehydroxy aromatic compound to thereby produce a colored image in theexposed areas.
 14. A process according to claim 13 wherein said image isfixed in said film.
 15. A process according to claim 13 wherein anaromatic amine is included in said solution.
 16. A process according toclaim 13 wherein the hydroxy aromatic compound is substituted with anamino radical.
 17. A process according to claim 13 wherein a metallicsalt is added to said solution.